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Using Coral Colonies to Predict the Growth of COVID-19

Wikipedia Commons
Wikipedia Commons

There has been a notable lack of transparency from local officials when it comes to data surrounding Hawaii’s coronavirus pandemic.


As HPR has previously reported, the models used by state Department of Health to predict the trajectory of local COVID-19 infections have not been released to the public.


Amid a surge in new cases of the virus and recently enacted social restrictions, a new model is now shedding light on how the SARS CoV-2 virus spreads in the islands, but it did not come from government officials. It was designed by a scientist at the University of Hawaii using an unlikely reference: local coral colonies.

Credit Joshua Madin / J. Madin Lab/Hawaii Institute of Marine Bioloy
Projected growth in total CVOID-19 cases if no action were taken to reduce spread of the virus. The curve shows that Hawaii recently entered the so-called exponential phase of growth, in which the number of cases increases rapidly.


Josh Madin is a marine biologist at the Hawaii Institute of Marine Biology on Coconut Island. Normally, his research normally focuses on problems like coral bleaching and mapping coral colonies. As it turns out, the mathematical models used to predict the growth of corals also work pretty well for modeling spread of a virus like the one that causes COVID-19.


“We use models like this all the time in corals; we’re usually trying to get corals to grow,” Madin said in an interview.


“But in the case of COVID-19, it’s the opposite. You want to figure out how to slow it down.”


While it’s not an exact comparison, there are some similarities between the seemingly disparate organisms. A virus needs a host in order to reproduce, just like coral colonies need a reef on which to grow.


Madin released his COVID growth projection on Twitter when Hawaii began to see new daily case numbers in the triple digits. The model shows that without swift intervention to reduce new infections, the virus would quickly grow out of control. A time-lapse graph shows that without intervention to stop the spread, the trendline for new cases will be almost vertical. 


“That’s what you call the exponential phase of population growth, and that’s kind of the scary phase,” Madin explained.


“It’s really hard to slow it down from this point because whatever you do know will take a couple of weeks to unfold.”

Credit Joshua Madin / J. Madin Lab/Hawaii Institute of Marine Bioloy
Three scenarios showing the spread trajectory if Hawaii were able to reduce to zero cases in 14 days, in 1 month, and in 2 months. Madin says that taking 2 months to reach zero cases results in nearly doubles the total number of cases, compared to reaching zero cases in 14 days.


According to the state Department of Health, the number of new COVID-19 cases fell last week, but later climbed again, before declining yesterday. New cases remain in the triple-digits.


While fewer new cases is certainly a positive sign, it does not mean Hawaii is out of danger and social restrictions can be relaxed. As Madin points out, even a falling number of new cases still represents more infections occurring in the community. The virus cannot be considered under control until the number of daily new cases drops dramatically.


 “What you really want to do is get that back down to around zero,” Madin notes.


“That’s when you start plateauing and you’re not going to see the virus increasing anymore.”


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